Secondary battery.



Patented July 4, 1905.

ISIDOR KITSEE, OI? i i-filial DELPHIA, PENNSYLVANIA.

SPECIFICATION forming part of Letters Patent No. 793,881, dated July 4:1905.

Application filed March 17,1893. Serial No. 466,533.

To aZZ whom, it may concern/.-

Be it known that I, ISIDOR Krrsnn, a citizen of the United States,residing at Philadelphia, in the county of Philadelphia and State ofPennsylvania, have invented certain new and useful Improvements inSecondary Batteries, of which the following is a specification.

My invention relates to the positive-pole electrodes of secondarybatteries.

In secondary cells the electrodes of which have metallic compounds as avehicle for the electric energy the positive-pole electrode becomesactive only after the material has undergone a higher oxidation. Incells Where a compound of lead is used such compounds have to reach thehighest oxidation before the cell is capable of storing theelectricenergy. In the act of charging the current tends to inoculate,so to speak, the active oxygen in the pores of the highly-oxidizedmaterial. If such charging is continued after the limit of'storing theenergy is reached, the liberated gases attack the surface of theelectrode to such an extent that the material disintcgrates. The sameresult follows if the rate of the charging-current is greater than thecapacity of the electrode to assimilate the liberated gas; but even ifthe charge rate is not abnormal and the charge only kept up till thesaturation-point is reached the disintegration of the active material isonly a question of time, for the simple reason that the active materialhaving once attained its highest state of oxidation never returns to thestate of low oxidation in its entirety, but only loses its surplusactive oxygen. ".l.hc next chargirig-current therefore meets materialalready in the highest state of oxidation, and the tendency o'fevery newchargeis to disintegrate more and more the already highlyoxidized activematerial. Careful cxperiments have established the fact that the rate ofcharge which an electrode can withstand without deterioration decreaseswith the number of charges and that the capacity for storing bears acertain relation to the overoxidation of the active material.

The object of my invention is to restore to the active material ofelectrodes having already undergone charging and discharging processesthe resisting and storing powerthe vitality, so to say--it originallypossessed.

The active material on the positive or oxygen plate in a secondary cellof the lead type is through the action of the electric current convertedinto a peroxid, (Pb()e,)tl1l slight traces of sulfate of lead remainpartially as a binding material in the mass if either thecharging-current is too high or of too long duration, or if the chargingand discharging has taken place rather too often then the followingstate exists:

First. lVhcreas through the charging-current even an oxid of lead (PbgO)is converted into a peroxid the act of discharging does not reduce thishigh oxid entirely, but it only reduces the mass in a manner so that atthe surface a compound of high oxid intermixed with low oxids andsulfates is formed, giving such a complex result when analyzed that theabove quotation does not take in every phase of the resultingconversion. The sulfate is formed through the reduction of the peroxidto the proto state and then eonverting the protoxid into a sulfate salt.The

farther toward the center, the less the rcduction, and if the mass is ofconsiderable thickness, it will be found that even after a dis charge to1.7 volts has taken place, the center still consists mostly of a peroxidwith very slight traces of sulfate.

Second. If such a material. is again subjectcd to the charging-currel'it, and more s )ec-- ially if this charging-current is of acomparative high density. then three actions take place --(a) theformerly redueed particles are again brought to the high oxidation, (I!)the sulfate molecules are driven off from the surface, (0) the innercenter is oxidized to an extent so as to drive out entirel all traces ofsulfate and bring the mass to a state wherein the ilbllu is converted,even if only momentarily, into a higher oxid. It has to be stated thatthis higher oxidation is only due to the overcharging of the activematerial and is very unstable; but it causes the material to becomesoft, losing its adherence and gradually going off into the liquid as afinely-divided powder. This state is dreaded by all manufacturers andusers of secondary batl teries, and yet it cannotbe prevented, because,as said before, every new charging-current finds the active material ina higher state of 1 oxidation and with less traces of sulfate, andtherefore in a condition more liable to disintegration. To obviate thisdifliculty is the aim of my invention. and .I obtain the result by themethod described in this application, which method consists therein thatthe overoxidized material is brought in contact with the materialcapable of producing a chemical change in said overoxidized material ina manner so that part of the overoxidized particles are partiallydeoxidized and partially converted either into a sulfate or chlorid, asthe case may be, and through this change the mass of active material isbrought again to its former solidity and can again withstand the forceof the charging-current without undue deterioration.

The underlying principle of my invention is the treatment of theelectrode the active material of which has already undergone theoxidizing process through the action of the current with a material theaflinity for oxygen of which is greater than the power said activematerial possesses for retaining its own state of high oxidation, or, inother words, I subject the high oxid of the electrode to a reducingprocess. The reduction can be accomplished through different agencies. Asimple Way of reducing the high oxid to a lower state is subjecting theelectrode to the action of heat; but the difliculty arises that theactive material being part of the whole electrode cannot be subjected toa temperature higher than the metallic conductor or non-metallic supportcan withstand. The process therefore is a very slow one; but where timeis of no consideration the reducing process with the aid of dry heat canbe done by suspending the electrode in a hermetically-sealed recess ofone of the usual drying devices subjected to the action of heat. Greatcare should also be taken in raising the temperature, for the reasonthat, especially Where the active material is of considerable thickness,spurting of the same follows if the deoxidation is too quick or too faradvanced, and I found it necessary, first, to take during the reducingprocess frequent readings of an inserted thermometer; second, tointerrupt the process at intervals and to renew the same only afterexposing the electrode to a cooler temperature. In moist state andwithout the action of heat different chemical combinations can be used.Chlorid of sodium, for instance, applied to the electrode moist with thesulfuric acid, reduces the high oxid by forming with part of the chlorincontained in the sodium and chlorid of lead, the chlorid of sodiumforming then a sulfate of soda. In other words, the chlorid of sodium(NaCl) dissolved in the electrolyte (HgSOr) plus water forms a sulfateof soda (NZLZOSOJi) lus water by taking part of the oxygen contained inthe high oxid of lead and part of the sulfur contained in theelectrolyte, and the so-reduced high oxid of lead combines with part ofthe chlorin released through the forming of said sulfate salt. Thedeoxidizing process can also be carried out through the agency of gases.If sulfurous gas is used, it is only necessary to inclose the electrodein a vessel and to introduce the gas into the vessel. The activematerial should be moist throughout. The highly-oxidized material willcombine with the gas, forming a sulfate; but if the active material isof considerable thickness it is best to repeat the process, each timemoistening the electrode with water or very diluted sulfuric acid, itbeing understood that the sulfurous gases will form in the presence ofoxygen and moisture a sulfate. Great care should be exercised. Theactive material is apt to be raised to too high a temperature in the actof undergoing the chemical change, and if the gas is introduced in aconcentrated state and the electrode allowed to become dry it happensthat the raised temperature is sufficient to break up the wholeelectrode, to soften the support if such is of hard rubber, and evenattack the metallic conductor; but I do not limit myself to thedescribed chemicals, as many other compounds are capable through theirgreat affinity for oxygen to withdraw one or more atoms of the gas fromits combination with the material of the electrode.

To obviate misunderstandings, I remark right here that wherever I use inthe application or claims the word reducing or renovating in connectionwith the active material of the electrode I understand under it theaction through which the material loses a greater or lesser part of itsoxygen, no matter if in consequence of it said material comblues withanother element or compound or not.

Having now described my invention, What I claim as new, and desire tosecure by Letters Patent, is-

1. The method of restoring the usefulness of overcharged active materialin secondary cells which consists in bringing said active material intocontact with a solution adapted to in part reduce said active materialto a lower oxid and in part change the same to a salt adapted to act asbinder for the particles of said lower oxid.

2. The method of treating positive-pole electrodes for secondary cellswhich consists in bringing said electrodes in contact with a compoundadapted to reduce part of the active material of said electrodes and toconvert part of said active material into a salt adapted to serve as abinder for the oxid particles.

3. The method of renovating electrodes, having served as positive-poleelectrodes in secondary batteries, which consists in bringing thehighly-oxidized active material to a state of low oxidation, and capableof converting part of the oxidized material into a salt adapted to actas binder.

In testimony that .l. claim the foregoing as my invention I hereuntosign my name this ltll day of August, 1890.

lZSIDOR KITSEE.

Witnesses:

DAVID S. "WILLIAMs, WALTER Alien-ass.

